[IPFIX] Options Templates, Templates, and related Data Sets sent in separate transport sessions

[Garri Djavadyan <[e-mail]>]

Hi IPFIX experts,


Recently, my colleagues and I faced an IPFIX exporter implementation
that sends IPFIX messages with the Template and related Data Sets in
one transport UDP session and the Options Template and related Data
Sets in another transport UDP session (sourced from a different UDP
port) to the same IPFIX collector port.

While trying to understand this behaviour, I checked RFC7011 and a few
related RFCs but could not find any notes suggesting use cases when it
might be necessary. Also, I could not find any notes prohibiting this.

However, we know of at least one use case when sending the
aforementioned 4 IPFIX messages over 2 separate transport sessions is
undesirable. For example, when multiple self-sufficient IPFIX
collectors are listening on the same UDP socket using the socket option
SO_REUSEPORT (for horizontal scaling), the kernel-level load-balancing
algorithm can distribute 2 related sessions of the same exporter to
different processes. As a result, the process receiving the Flow
Records, cannot process them properly without the related Options. In
theory, it can also happen in the environments where layer-4 load-
balancers are used to distribute transport UDP sessions between IPFIX
collecting hosts.

Considering this, could you please help answer the following question?

Did I interpret the IPFIX RFCs correctly and the mentioned exporter's
behaviour is a compliant implementation?

There is a note in the "Template Management" section 8 of RFC7011
saying:

   Options Templates and Templates that are related or interdependent
   (e.g., by sharing common properties as described in [RFC5473])
   SHOULD be sent together in the same IPFIX Message.

but the Templates and the Options Templates in the case that I
mentioned are not interdependant by the common properties per RFC5473.



Thank you in advance!


Kind regards,
Garri Djavadyan